Flame resistant rendering heat treating device, and operation method for the device

ABSTRACT

A heat treatment apparatus for oxidation having an oven for oxidation having a heat treatment chamber having a plurality of slits through which fiber strands running horizontally leave or returned strands enter and capable of sending hot air vertically from above the fiber strands to allow the fiber strands to have oxidation, and a device for feeding hot air into the heat treatment chamber, and a plurality of returning rollers which are provided at the two outsides of the oven for oxidation and which return the fiber strands entering and leaving through said slits, into the oven for oxidation, wherein each gap formed between fiber strands and each side wall of heat treatment chamber parallel to the running direction of fiber strands running in the heat treatment chamber, or each gap formed between fiber strands and each channeling-preventing plate interposed between the side wall and the fiber strands in parallel to the running direction of fiber strands is set at 150 mm or less. The slits may be provided with a device for injecting hot air into the heat treatment chamber.

TECHNICAL FIELD

The present invention relates to a heat treatment apparatus foroxidation, used in production of polyacrylonitrile-based oxidation fiber(flame-resistant fiber). More particularly, the present inventionrelates to an apparatus used for subjecting polyacrylonitrile-basedfiber strands or the like to a heat treatment for oxidation, as well asto an operating method of tile apparatus. The oxidation fiber isimportant as a heat-resistant fiber or as a material for production ofpolyacrylonitrile-based carbon fiber.

BACKGROUND ART

Polyacrylonitrile-based oxidation fibers have been produced bysubjecting a polyacrylonitrile-based fiber to a heat treatment foroxidation in an oxidizing atmosphere of 200 to 300° C.

The reaction taking place in the heat treatment ofpolyacrylonitrile-based fiber for oxidation is an exothermic reactionwherein oxidation and cyclization take place simultaneously. A heattreatment at a high temperature results in a high reaction rate and ashort treatment time. When the heart treatment for oxidation isconducted rapidly, however, the heat generated in the oxidation reactionis accumulated in the fiber and the fiber-inside temperature increases.As a result, an uncontrollable reaction which is accompanied by yarnbreakage and firing, tends to be invited.

Further, the heat treatment for oxidation is ordinarily conducted forstrands which are each formed as a bundle of a large number of fibers.When a large number of strands are simultaneously subjected to the heattreatment for oxidation for higher production efficiency, it isimpossible to obtain oxidation fiber strands at a high temperature in ashort time without efficiently removing the generated reaction heat fromthe fibers, because heat accumulates easily in the strands.

Since the time required for heat treatment for oxidation is long and theenergy required therefor is very large, a further improvement inproductivity is needed in the step of heat treatment for oxidation.

FIG. 10 is a schematic drawing showing a conventional heat treatmentapparatus for oxidation. (A) is a front section, (B) is a side section,and (C) is a top section.

In FIG. 10(A), 52 is a heat treatment apparatus for oxidation. In a heattreatment chamber 54 thereof run plural steps of paths 57 a, 57 b, 57 c,. . . 57 x each formed by a large number of strands 56 arrangedhorizontally. As shown in FIG. 10(B), the strands 56 are returned bygiven sets of returning rollers 58 provided outside the heat treatmentchamber 54 and are fed into the heat treatment chamber 54 repeatedly.

As shown in FIG. 10(B), the strands 56 forming the plural steps of pathsleave and enter the heat treatment chamber 54 through the slits 64 a, 66a, 66 b and 64 b respectively formed in the outer wall 60 a, inner wall62 a, inner wall 62 b and outer wall 60 b of the heat treatmentapparatus for oxidation.

As shown in FIG. 10(C), inner side walls 68 a and 68 b are formed at theboth sides of heat treatment chamber 54.

In the left half of the heat treatment chamber 54, an outer side wall 69a is formed outside the inner side wall 68 a, and a hot air circulationduct 74 a is formed between the inner side wall 68 a and the outer sidewall 69 a. As shown in FIG. 10(A), the hot air circulation duct 74 aconnects an upper duct 70 and a lower duct 72 both of the heat treatmentchamber 54.

A heater 76 a provided in the hot air circulation duct 74 a generateshot air, and the hot air is sent into the upper duct 70 by a fan 78 aand further into the heat treatment chamber 54. Then, the hot air passesbetween the strands 56 running in a path state and is sent downward. Atthis time, the strands are heat-treated for oxidation. Incidentally, thehot air heats the strands and also has the role of heat removal.

Then, the hot air passes through the lower duct 72 and is sent into thehot air circulation duct 74 a. The hot air is heated therein by theheater 76 a. This operation is repeated.

In the left half of the heat treatment chamber 54 shown in FIG. 10(C),an outer side wall 69 b is formed outside the inner side wall 68 b.Between the inner side wall 68 b and the outer side wall 69 b is formeda heat-insulating air chamber 80 a.

Meanwhile, the right half of the heat treatment chamber 54 shown in FIG.10(C) is formed skew-symmetrically to the left half. That is, betweenthe inner side wall 68 a and the outer side wall 69 a is formed aheat-insulating air chamber 80 b. Similarly, between the inner side wall68 b and the outer side wall 69 b is formed a hot air circulation duct74 b connecting the upper duct 70 and the lower duct 72 both of the heattreatment chamber 54. 76 b is a heater and 78 b is a fan.

This heat treatment apparatus is covered, at the circumference, with aheat-insulating material for an enhanced heat efficiency.

Even in such a heat-insulating structure, the temperature, for example,in the vicinity of the inner side walls 68 a and 68 b of the heattreatment chamber 54 is lower than the average temperature inside theheat treatment chamber 54. As a result, the rate of heat treatment foroxidation, of the strands near the inner walls 68 a and 68 b is low andthe heat treatment of strands for oxidation do not take place uniformly.In order to avoid this problem, strands 56 are ordinarily allowed to runabout 200 mm apart from the side walls 68 a and 68 b in ordinary heattreatment apparatuses for oxidation.

Meanwhile, in the heat treatment chamber 54, a large number of strands56 forming paths may be allowed to run in one zone wherein the strands56 are arranged uniformly. However, running of paths in a plurality ofzones [two zones 59 a and 59 b in FIG. 10(A)] in place of one zone, witha given gap X taken between two neighboring zones allows easierhandling.

For example, when strands forming paths are allowed to run in one zoneand when troubles such as fiber breakage and the like occur, the brokenpiece of fiber coils around a nearby strand, resulting in worsening oftrouble and possible spread of the damage to the whole strands. Further,manual operation may be needed for the troubled strands. For thesereasons, it is preferred to divide paths into a plurality of zones witha given gap taken between two neighboring zones.

Therefore, in ordinary heat treatment apparatuses for oxidation, strands56 forming paths are divided into a plurality of zones, the gap betweenthe inner side wall and paths is kept at about 200 mm, a gap of about200 mm is taken between two neighboring zones, and a heat treatment ofstrands for oxidation is conducted.

When, in the above heat treatment apparatus for oxidation, strandsrunning in a state of horizontal plural steps of paths arrangedvertically are heat-treated for oxidation in the heat treatment chamber,if the number of strands in the heat treatment chamber is increased forhigher productivity, hot air receives an increased resistance and thespeed of hot air passing through paths is reduced significantly.Resultantly, the strands undergo insufficient cooling. As a result, heatis generated in the strands and, moreover, breakage of fiber due togenerated heat occurs. Further, the broken fiber coils around the fiberof other strand, resulting in worsening of trouble. Incidentally, thisproblem in heat treatment of polyacrylonitrile-based fiber for oxidationmay develop into fire being generated. Because of the occurrence of sucha serious problem, significant improvement in productivity of oxidationfiber has heretofore been impossible.

DISCLOSURE OF THE INVENTION

The present inventor considered that the reduction in speed of hot airduring its passing through strand paths is caused by the concentrationof hot air in between paths and inner side wall and between zones. Thespeed of hot air passing through paths tends to decrease significantlyin lower paths, in particular, and the breakage of fiber occursfrequently in these lower paths.

In order to prevent such fiber breakage, a countermeasure such aslowering the inside temperature or the like of heat treatment chamber isnecessary. The lowering inside temperature of heat treatment chamber,however, results in lower reaction rate and consequently in lowerproductivity, which is contrary to intended productivity improvement.

Further, in subjecting strands to a heat treatment for oxidation usingthe above heat treatment apparatus for oxidation, there is a problem inthat hot air leaks from the slits formed for leaving and entering ofstrands from and into the heat treatment chamber.

According to an experience, when the speed of hot air passing throughthe uppermost strand path located at the upstream of hot air is, forexample, 1.8 m/sec, the speed of hot air passing through intermediatestrand paths located at the downstream of hot air may drop to 0.3 m/sec.In such a case, it is considered that in lower paths, the reaction heatgenerated by the oxidation of strands tends to be removed less by hotair.

Further, the reaction heat generated by the strands of upper pathslocated at the upstream of hot air is carried by hot air to thedownstream of hot air. Hence, it was considered that the strands oflower paths causes heat build-up and reach a high temperature, makingimpossible uniform heat treatment for oxidation. In such a case, it ispossible that lower strands give rise to an uncontrollable reaction andfiring.

SUMMARY OF THE INVENTION

The present invention has been completed based on the aboveconsiderations.

Hence, the present invention aims at providing a heat treatmentapparatus for oxidation which can uniformly conduct a heat treatment ofstrands for oxidation and which can give improved productivity withoutquality deterioration, and an operating method of the apparatus.

The present invention which achieves the above aim, lies in thefollowing.

-   [1] A heat treatment apparatus for oxidation having:    -   an oven for oxidation having a heat treatment chamber having a        plurality of slits through which fiber strands running        horizontally leave or returned strands enter and capable of        sending hot air vertically from above the fiber strands to allow        the fiber strands to have oxidation, and a means for feeding hot        air into the heat treatment chamber, and    -   a plurality of returning rollers which are provided at the two        outsides of the oven for oxidation and which return the fiber        strands entering and leaving through said slits, into the oven        for oxidation,        wherein each gap formed between fiber strands and each side wall        of heat treatment chamber parallel to the running direction of        fiber strands running in the heat treatment chamber, or each gap        formed between fiber strands and each channeling-preventing        plate interposed between the side wall and the fiber strands in        parallel to the running direction of fiber strands is set at 150        mm or less.-   [2] A heat treatment apparatus for oxidation according to the above    [1], wherein the channeling-preventing plate has air-passing holes.-   [3] A heat treatment apparatus for oxidation according to the above    [1], wherein the oven for oxidation comprises:    -   a heat treatment chamber wherein hot air passes from the above        toward the bottom,    -   an upper duct formed at the top of the heat treatment chamber,    -   a lower duct formed at the bottom of the heat treatment chamber,        and    -   a hot air circulation duct connecting the upper duct and the        lower duct.-   [4] A heat treatment apparatus for oxidation according to the above    [3], wherein an air rate-controlling member is provided in the hot    air circulation duct.-   [5] A heat treatment apparatus for oxidation according to the above    [3], wherein hot air circulation means are provided at the top and    bottom of the hot air circulation duct.-   [6] A heat treatment apparatus for oxidation according to the above    [5], wherein each hot air-circulation means is a fan or a blower.-   [7] A heat treatment apparatus for oxidation according to the above    [6], wherein the blower is a multi-blade blower having two inlets    for hot air.-   [8] A heat treatment apparatus for oxidation according to the above    [1], wherein air-passing members having an opening ratio of 50% or    more are provided above lower air-passing plates provided at the    bottom of the heat treatment chamber and apart from the lower    air-passing plates by 20 mm or more.-   [9] A heat treatment apparatus for oxidation having:    -   an oven for oxidation having a heat treatment chamber having a        plurality of slits through which fiber strands running        horizontally leave or returned strands enter and capable of        sending hot air vertically from above the fiber strands to allow        the fiber strands to have oxidation, and a means for feeding hot        air into the heat treatment chamber, and    -   a plurality of returning rollers which are provided at the two        outsides of the oven for oxidation and which return the fiber        strands entering and leaving through said slits, into the oven        for oxidation,        wherein each gap formed between fiber strands and each side wall        of heat treatment chamber parallel to the running direction of        fiber strands running in the heat treatment chamber, or each gap        formed between fiber strands and each channeling-preventing        plate interposed between the side wall and the fiber strands in        parallel to the running direction of fiber strands is set at 150        mm or less and a heating means is provided at the side walls or        in the slits.-   [10] A heat treatment apparatus for oxidation according to the    above-noted item [9], wherein the heating means is a hot air duct    formed outside each side wall of the heat treatment chamber.-   [11] A heat treatment apparatus for oxidation according to the    above-noted item [9], wherein the heating means is a heater formed    each side wall of the heat treatment chamber.-   [12] A heat treatment apparatus for oxidation according to the above    [9], wherein the heating means is nozzles for feeding hot air into    the heat treatment chamber, provided in all or part of the plurality    of slits.-   [13] A heat treatment apparatus for oxidation according to the    above-noted item [12], wherein the hot air has a temperature higher    than the temperature of the heat treatment chamber.-   [14] A heat treatment apparatus for oxidation according to the    above-noted item [12], wherein the nozzles have a mechanism of    feeding, into the heat treatment chamber, not only the hot air    injected from the nozzles but also the air present in the vicinity    of each nozzle and drawn by said hot air.-   [15] A heat treatment apparatus for oxidation according to the    above-noted item [12], wherein the nozzles are provided only in the    slits through which each fiber strand enters the heat treatment    chamber.-   [16] A heat treatment apparatus for oxidation according to the    above-noted item [12], wherein at least one of lower slits    corresponding to 70% of the total slits has a nozzle capable of    injecting air outside the heat treatment chamber.-   [17] An operating method of a heat treatment apparatus for oxidation    having:    -   an oven for oxidation having a heat treatment chamber having a        plurality of slits through which fiber strands running        horizontally leave or returned strands enter and capable of        sending hot air vertically from above the fiber strands to allow        the fiber strands to have oxidation, and means for feeding hot        air into the heat treatment chamber, and    -   a plurality of returning rollers which are provided at the two        sides of the oven for oxidation and which return the fiber        strands entering and leaving through said slits, into the oven        for oxidation,        wherein each gap formed between fiber strands and each side wall        of heat treatment chamber parallel to the running direction of        fiber strands running in the heat treatment chamber, or each gap        formed between fiber strands and each channeling-preventing        plate interposed between the side wall and the fiber strands in        parallel to the running direction of fiber strands is set at 150        mm or less and the plurality of slits are each provided with a        nozzle capable of injecting hot air inside the oven for        oxidation,    -   in which the operating method the speed of the hot air fed from        the nozzles is controlled and thereby the speed of the hot air        passing through the fiber strands other than the uppermost fiber        strands is kept at 20% or more of the speed of the hot air        passing through the uppermost fiber strands.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are each a schematic front sectional view showing anexample of the heat treatment apparatus for oxidation according to thepresent invention.

FIG. 5 is a schematic section showing other example of the heattreatment apparatus for oxidation according to the present invention,wherein (A) is a front perspective view and (B) is a side perspectiveview.

FIG. 6 is a plan section of the apparatus for oxidation shown in FIG. 5.

FIG. 7 is an enlarged view of the portion A of FIG. 5(B).

FIG. 8 is a schematic section showing other example of nozzle.

FIG. 9 is a schematic section showing still other example of nozzle.

FIG. 10 shows an outline of a conventional heat treatment apparatus foroxidation, wherein (A) is a front section, (B) is a side section and (C)is a plan section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention includes a heat treatment apparatus 2 foroxidation; a heat treatment chamber 4; a strand 6; side walls 8 a, 8 ban upper hot air duct 10; a lower hot air duct 12; a hot air circulationduct 14; a space 16; a heater 18; a fan 20; a gap P; a heat treatmentchamber 22; inner side walls 24 a, 24 b; hot air ducts 26 a, 26 b; aheat treatment apparatus 28 for oxidation; outer side walls 30 a, 30 b;a strand 32; a heat treatment apparatus 48 for oxidation; side walls 44a, 44 b; heating means 46 a, 46 b; a strand 50; a path 500; zones 510,512; a distance L; a distance M; a distance N; an oven 102 foroxidation; a front outer wall 104 a; a front inner wall 106 a; a backinner wall 106 b; a back outer wall 104 b; slits 108 a, 108 b; a leftouter side wall 112 a; a left inner side wall 114 a; a right inner sidewall 114 b; a right outer side wall 112 b; an upper outer wall 116 a; alower outer wall 116 b; an upper air-passing plate 118 a; a lowerair-passing plate 118 b; a heat treatment chamber 120; an upper duct122; a lower duct 124; a front half H; hot air circulation ducts 126 a,126 b; heat-insulating air chambers 128 a, 128 b; a back half I; astrand 130; returning rollers 132 a, 132 b; a distance R; a distance S;a distance T; a channeling-preventing plate 138 a; achanneling-preventing plate 138 b; a channeling-preventing plate 138 c;a hot air circulation means 142 a; a hot air circulation means 142 c; anair speed-controlling member 140 a, 140 b; an air-passing member 144; aheat treatment chamber wall 202; an outer wall 204; an inner wall 206; aslit 208; a strand 210; an upper hot air duct 212; an lower hot air duct214; an upper nozzle 216; a lower nozzle 218; an angle of intersectionθ; an air speed controlling plate 220, 222; heat treatment chamber walls302, 402; slits 308, 408; upper nozzles 316, 416; and lower nozzles 318,418.

BEST MODE FOR CARRYING OUT THE INVENTION

(First Mode)

The present invention is described in detail below with reference toFIGS. 1 to 3.

FIG. 1 is a schematic front sectional view showing an example of theheat treatment apparatus for oxidation according to the presentinvention.

In FIG. 1, 2 is a heat treatment apparatus for oxidation wherein a heattreatment chamber 4 is formed therein and a large number of strands 6are running in the heat treatment chamber 4. (In FIG. 1, the runningdirection of strands is vertical to the paper surface.) The strands 6are parallel to each other and form a plurality of horizontal paths(seven paths in FIG. 1). These paths are arranged from upward todownward apart from each other by a given distance. The strands 6forming the paths are returned by given pairs of returning rollers (notshown in FIG. 1) provided outside the heat treatment chamber 4, and arefed into the heat treatment chamber 4 repeatedly.

Side walls 8 a and 8 b of the heat treatment chamber 4 are parallel tothe running direction of the strands 6. Outside the side wall 8 a isformed a hot air circulation duct 14. Between the side wall 8 a and thehot air circulation duct 14 is formed a space 16. An upper hot air duct10 and a lower hot air duct 12 both of the heat treatment chamber 4 areconnected by the hot air circulation channel 14. The upper hot air duct10, the lower hot air duct 12 and the hot air circulation duct 14constitute a hot air-feeding means.

A heater 18 is provided in the hot air circulation duct 14. Hot airheated by the heater 14 is passed, by a fan 20, through the upper hotair duct 10 of the heat treatment chamber 4, sent into the heattreatment chamber 4, and flows down in the heat treatment chamber 4. Atthat time, the strands 6 running in a state of the above-mentioned pathsare heat-treated for oxidation. Then, the hot air is passed through thelower hot air duct 12, sent to the bottom of the hot air circulationduct 14, and is returned to the heater 18. This operation is repeated.

In the heat treatment chamber 4 of the heat treatment apparatus foroxidation, a gap P between side wall 8 a or 8 b and strand at end ofpath is set to be 150 mm or less, preferably at 50 mm or less, morepreferably at 5 to 20 mm. By thus setting the P at 150 mm or less,concentration of hot air in each gap between path and side wall can beprevented. Since the hot air passes over the path surfaces uniformly,the reduction in hot air speed which has heretofore arisen as the hotair moves from upper paths toward lower paths, can be minimized.

FIG. 2 shows other example of the heat treatment apparatus for oxidationaccording to the present invention. In this heat treatment apparatus 28for oxidation, outer side walls 30 a and 30 b are added respectivelyoutside of inner side walls 24 a and 24 b of a heat treatment chamber22. Between the inner side wall 24 a and the outer side wall 30 a andbetween the inner side wall 24 b and the outer side wall 30 b are formedhot air ducts 26 a and 26 b as a side wall-heating means for preventionof side wall temperature reduction. Further, a gap P between inner sidewall 24 a or 24 b and strand at end of path is set at 150 mm or less,preferably at 50 mm or less, more preferably at 5 to 20 mm. Otherconstitution is the same as in the heat treatment apparatus foroxidation shown in FIG. 1.

In the heat treatment apparatus 28 for fame resistance shown in FIG. 2,the temperature reduction of the side walls 24 a and 24 b can beprevented because the hot air ducts 26 a and 26 b are provided as a sidewall-heating means.

Incidentally, the gap between side walls of double structure, i.e. eachwidth of hot air ducts 26 a and 26 b is not critical but is preferred tobe ordinarily 100 to 200 mm.

In the heat treatment apparatus 28 for oxidation, strands 32 running inthe heat treatment chamber 22 receive thermal load uniformly; there issufficient heat removal over the entire paths; and the productivity ofoxidation fiber can be made high.

FIG. 3 shows still other example of the heat treatment apparatus foroxidation according to the present invention.

This heat treatment apparatus 48 for oxidation is provided with heatingmeans 46 a and 46 b outside side walls 44 a and 44 b. The heating meansare not critical and can be exemplified by an electric heater and asteam heater. By the heating means, the difference between the heattreatment chamber temperature and side wall temperature can be set at10° C. or less. Further, a gap P between side wall 44 a or 44 b andstrand 50 at end of path is set at 150 mm or less, preferably at 50 mmor less, more preferably at 5 to 20 mm.

Other constitutions are the same as in the heat treatment apparatusesfor oxidation, shown in FIGS. 1 and 2.

Owing to the heating means 46 a and 46 b, the difference between heattreatment chamber temperature and side wall temperature can be madesmall (10° C. or less) and the temperature reduction of strand 50 ateach end of path can be prevented.

Each of the above heat treatment apparatuses for oxidation isconstituted so that the gap P between side wall and strand constitutingpath become 150 mm or less; therefore, there is no concentration of hotair in the gap P. Since hot air passes between strands uniformly overthe entire paths, the reduction in hot air speed from upper paths tolower paths can be prevented.

The above description on each heat treatment apparatus for oxidation wasmade on a case wherein paths are not divided into a plurality of zones.When, as shown in FIG. 4, paths 500 are divided into a plurality ofzones (two zones 510 and 512 in FIG. 4), the distance between zones (Lin FIG. 4) and the distances between zone and side wall (M and N in FIG.4) are each set at 150 mm or less, preferably at 50 mm or less, and morepreferably at 5 to 20 mm.

(Second Mode)

The present invention is described in detail below with reference toFIGS. 5 to 9.

FIG. 5 is a schematic section showing an example of the heat treatmentapparatus for oxidation according to the present invention, wherein (A)is a front perspective view and (B) is a side perspective view. FIG. 6is a plan section of the apparatus of the same apparatus. FIG. 7 is anenlarged view of the portion shown by A of FIG. 5(B). Incidentally, inthis example, the indication of direction was made mainly based on FIG.5(A); the front of the paper surface of FIG. 5 is referred to as “front”and the back of the paper surface is referred to as “back”; and theleft, right, upper and lower of the paper surface are referred to as“left”, “right”, “upper” and “lower”, respectively.

In FIG. 5, an oven 102 for oxidation is shown. From the front of theoven 102 for oxidation of FIG. 5(A) toward the back, that is, from theleft of FIG. 5(B) toward the right, a front outer wall 104 a, a frontinner wall 106 a, a back inner wall 106 b, and a back outer wall 104 bare provided. In these walls, slits 108 a are formed being of the samenumber as that of paths from the front outer wall 104 a to the frontinner wall 106 a. Also, slits 108 b are formed by the same number asthat of paths from the back outer wall 104 b to the back inner wall 106b.

In the oven 102 for oxidation are formed, in the order of from the leftof FIG. 5(A) to the right, a left outer side wall 112 a, a left innerside wall 14 a, a right inner side wall 114 b and a right outer sidewall 112 b.

As shown in FIG. 5(A) and FIG. 5(B), in the oven 102 for oxidation areprovided, in the order of from the upper to the lower, an upper outerwall 116 a, an upper air-passing plate 118 a, a lower air-passing plate118 b and a lower outer wall 116 b.

A heat treatment chamber 120 is formed by being surrounded by the frontinner wall 106 a, the back inner wall 106 b, the left inner side wall114 a, the right inner side wall 114 b, the upper air-passing plate 118a and the lower air-passing plate 118 b.

An upper duct 122 is formed above the heat treatment chamber 120, thatis, in the area surrounded by the front outer wall 104 a, the back outerwall 104 b, the left inner side wall 114 a, the right inner side wall114 b, the upper outer wall 116 a and the upper air-passing plate 118 a.

A lower duct 124 is formed below the heat treatment chamber 120, thatis, in the area surrounded by the front outer wall 104 a, the back outerwall 104 b, the left inner side wall 114 a, the right inner side wall114 b, the lower outer wall 116 b and the lower air-passing plate 118 b.

In the front half H (FIG. 6) of the heat treatment chamber 120, outsidethe left inner side wall 114 a is provided a hot air circulation duct126 a connecting the upper duct 122 and the lower duct 124 both of theheat treatment chamber. Outside the right inner side wall 114 b isprovided a heat-insulating air chamber 128 a.

The back half I (FIG. 6) of the heat treatment chamber 120 isconstituted in contrast to the front half H. That is, outside the rightinner side wall 114 b is provided a hot air circulation duct 126 bconnecting the upper duct 122 and the lower duct 124 both of the heattreatment chamber, and outside the left inner side wall 114 a is formeda heat-insulating air chamber 128 b.

In FIG. 5(B), 130 is a polyacrylonitrile-based fiber strands. Thestrands 130 pass through slits 108 a formed from the front outer wall104 a to the front inner wall 106 a and through slits 108 b formed fromthe back outer wall 104 b to the back inner wall 106 b, and leave orenter the heat treatment chamber 120. In the heat treatment chamber 120run the strands 130 horizontally. The strands 130 are returned by givenpairs of returning rollers 132 a and 132 b provided outside the oven 102for oxidation and are fed into the heat treatment chamber 120 in a stateof a plurality of paths [five paths in FIG. 5(B)] arranged vertically.

Further, the strands 130 running in a state of paths are divided into aplurality of zones (two zones in FIG. 5) parallel to the runningdirection. The distance between zones (in FIG. 6, the distance R at thecenter of strands 130 running in a state of paths) and the distances Sand T between inner side wall 114 a or 114 b of heat treatment chamber20 and strands are each 100 mm or more, preferably 150 to 200 mm.

In the present example, in the gaps R, S and T are provided,respectively, channeling-preventing plates 138 a, 138 b and 138 c. Thechanneling-preventing plates are preferably provided for each path, thatis, all paths from path top to path bottom (five paths in this example).By providing the channeling-preventing plates in the gaps R, S and T,the gaps R, S and T are blocked; the gap between fiber strands runningin the heat treatment chamber in a state of zones andchanneling-preventing plate, or the gap between fiber strands and thechanneling-preventing plate interposed between fiber strands and sidewall in parallel to the running direction of fiber strands is set at 150mm or less, preferably at 50 mm or less, more preferably at 5 to 20 mm;and uniformization of the speed of hot air is aimed.

As the channeling-preventing plates 138 a, 138 b and 138 c, there can beused a plate of no air permeability, for example, a plate having nohole. However, in order to make more uniform the distribution of hot airspeed in each horizontal path, the channeling-preventing plates 38 a, 38b and 38 c are preferably a channeling-preventing plate having holes(air permeability), such as a punching plate, a wire net or the like.The channeling-preventing plates preferably have an opening ratio of 60%or less.

The plate of air permeability preferably has a hole diameter of 5 mm ormore. By allowing the plate to have a hole diameter of 5 mm or more, theplate is easy to clean and less plugged with fluff of strand.

The heat treatment apparatus for oxidation according to the presentinvention is provided with a hot air circulation means in each hot aircirculation duct, preferably at the top and/or bottom of each hot aircirculation duct. For example, as shown in FIG. 5(A), hot aircirculation means 142 a and 142 c can be provided between the upper duct124 and the hot air circulation duct 126 a both of the heat treatmentchamber 120 and between the lower duct 120 and the hot air circulationduct 26 a both of the heat treatment chamber 120.

As the hot air circulation means 142 a and 142 c, a fan, a blower or thelike can be used. In particular, a multi-blade blower having two hot airinlets is preferred.

By the hot air circulation means 142 c, hot air is sucked and recoveredfrom the lower duct 124 of the heat treatment chamber 120 into the hotair circulation duct 126 a. The recovered hot air is sent, by the hotair circulation means 142 a, from the hot air circulation duct 126 atoward the upper duct 122 of the heat treatment chamber 120.

As shown in FIGS. 5 and 6, it is possible to provide, in the hot aircirculation ducts 126 a and 126 b, air speed-controlling members 140 aand 140 b capable of controlling the speed of hot air passing throughthe above hot air circulation ducts.

The air speed-controlling members 140 a and 140 b can be exemplified bya damper. By controlling the air flow resistance of the airspeed-controlling members 140 a and 140 b, for example, the openness ofthe damper, it is possible to control the speed of sucking andrecovering hot air from the lower duct 124 of the heat treatment chamber120 into the hot air circulation duct 126 a or 126 b (not shown) by theabove circulation means 142 c, and the speed of feeding hot air from thehot air circulation duct 126 a or 126 b (not shown) into the upper duct122 of the heat treatment chamber 120 by the hot air circulation means142 a.

As described above, by controlling each output of the circulation means142 a and 142 c and each air flow resistance of the airspeed-controlling members 140 a and 140 b, the speed of the hot air canbe controlled so as to be appropriate to the strands of all paths.

It is preferred to provide air-passing members 144 at the bottom of theheat treatment chamber 120 so as to extend in the whole area of thebottom and, below them, lower air-passing plates 118 b so as to extendin the whole area of the bottom.

The air-passing members 144 are preferably a wire net, a grating or thelike all having an opening ratio of 50% or more.

The lower air-passing plates 118 b are intended to achieve a uniform hotair speed and are preferably a punching board or the like all having astraightening effect.

The air-passing members 144 are provided above the lower air-passingplates 118 b apart from the plates preferably by at least 20 mm.

The air-passing members 144 prevent cut strands generated during heattreatment for oxidation, from dropping and depositing on the lowerair-passing plates 118 b and blocking the holes of the lower air-passingplates 118 b.

When there are no air-passing members 144, the cut strands drop anddeposit on the lower air-passing plates 118 b. In this case, the holesof the lower air-passing plates 118 b are blocked and the speed of hotair decreases locally. It gives rise to heat build-up in strands beingsubjected to a heat treatment for oxidation, resulting in firing.Provision of the air-passing members 144 is effective for prevention ofsuch heat build-up and firing.

In the heat treatment apparatus for oxidation according to the presentinvention, it is possible to inject air or hot air into or outside theheat treatment chamber from at least one slit provided in each innerwall or outer wall through which strands pass for entering or leavingthe heat treatment chamber.

By injecting hot air from the slit into or outside the heat treatmentchamber, it is possible to control the speed of hot air flowing throughthe paths in the heat treatment chamber, control the temperature of hotair and minimizing the temperature distribution in the paths.

As to the form of injecting hot air from the slit into the heattreatment chamber, hot air may be injected into the heat treatmentchamber simply through the slit. Alternatively, a nozzle for injectinghot air may be provided along the slit and hot air may be injected fromthe nozzle. By injecting hot air from the nozzle, an air curtain isformed in the slit, whereby the air-tightness of the slit is enhanced.

It is also possible that outside air is drawn by the hot air injectedfrom the nozzle and is fed into the heat treatment chamber from the slitin order to supplement the speed of hot air.

An example of the above nozzle is shown in FIG. 7. In FIG. 7, 202 is aheat treatment chamber wall, 204 is an outer wall thereof, and 206 is aninner wall thereof. A slit 208 is formed from the outer wall 204 to theinner wall 206. Through this slit 208, a strand 210 enters and leavesthe heat treatment chamber. Above and beneath the slit 208 in the heattreatment chamber wall 202 are provided an upper hot air duct 212 and alower hot air duct 214. The ducts 212 and 214 are respectively providedwith an upper nozzle 216 and a lower nozzle 218 communicating with theabove ducts, with the front end of each nozzle directed toward insidethe heat treatment chamber. By feeding hot air into the ducts 212 and214, hot air is injected into the heat treatment chamber from the uppernozzle 216 and the lower nozzle 218. The angles of fixation of the uppernozzle 216 and the lower nozzle 218 are controlled so that the hot airsinjected from the nozzles intersect each other. The angle θ ofintersection is preferably 60 to 120°.

Incidentally, 220 and 222 are each an air speed-controlling plate. Byelevating or lowering the positions thereof, the speed of hot airinjecting from the nozzles 216 and 218 can be controlled.

In FIGS. 8 and 9 are shown other nozzle examples usable in the presentinvention. In FIGS. 8 and 9, 302 and 402 are each a heat treatmentchamber wall; 308 and 408 are each a slit; 316 and 416 are each an uppernozzle; and 318 and 418 are each a lower nozzle.

The nozzles may be fitted to all slits or part of them.

Also, the nozzles may be fitted with the front ends directed towardinside the heat treatment chamber and further with part of the frontends directed toward outside the heat treatment chamber. Part of the hotair passing through the heat treatment chamber is drawn by the airinjected from the nozzles whose front ends are directed toward outsidethe heat treatment chamber, and is discharged outside the heat treatmentchamber; thereby, the speed of hot air in the heat treatment chamber canbe controlled and penetration of outside air into the heat treatmentchamber can be prevented.

The nozzles whose front ends are directed toward outside the heattreatment chamber, are preferably fitted to at least one of the lowerslits which correspond to 70% of all the slits. By controlling the speedof air injecting from the nozzles fitted to each slit, it is possible tokeep the speed of the hot air passing through the lowermost path, at 20%or more, preferably 30% or more of the speed of the hot air passingthrough the uppermost path.

It is also possible to provide the nozzles injecting hot air only at theslits of the heat treatment chamber side through which strands enter theheat treatment chamber. In this case, a temperature reduction in thevicinities of these slits can be prevented effectively.

The temperature of the hot air injected from the nozzles is preferably150 to 300° C. The pressure of the hot air injected is desirably higherthan the pressure inside the heat treatment chamber 20 by 10 to 500 Pa.

In the above heat treatment apparatus for oxidation, the slits throughwhich polyacrylonitrile-based fiber strands leave and enter the oven foroxidation are provided with nozzles capable of feeding hot air into theheat treatment chamber. Therefore, leakage of hot air outside from theslits can be prevented effectively, hot air can be fed from the nozzles,and a reduction in hot air speed taking place from upper paths to lowerpaths can be prevented.

EXAMPLES Example 1

A heat treatment apparatus for oxidation shown in FIG. 4 was produced.The dimensions of the heat treatment chamber were length=15 m, breadth=2m, height=1.2 m, upper duct height=0.5 m, and lower duct height=0.3 m.Two returning rollers were provided at each side of the oven foroxidation. A multi-blade fan was provided in each of the upper and lowerhot air circulation ducts.

Gaps between zones and between each zone and inner side wall were set at1 cm. An electric heater was fitted to each side wall.

Into the apparatus were fed polyacrylonitrile-based fiber strands (1dtex, 24,000 fibers/strand). The feeding speed of strands was 300 m/hrand a hot air of 1.1 m/sec and 260° C. was fed to the uppermost path.

The electricity applied to the side wall heaters was controlled to keepthe temperature difference between side wall temperature and heattreatment chamber inside average temperature within 5° C. Thereby, thespeed of the hot air passing through intermediate paths could be kept at70% of the speed of the hot air passing through the uppermost path.

Example 2

A heat treatment apparatus for oxidation shown in FIG. 5 was produced.The dimensions of the heat treatment chamber were length=15 m, breadth=2m, height=1.2 m, upper duct height=0.5 m, and lower duct height=0.3 m.Two returning rollers were provided at each side of the oven foroxidation. A multi-blade fan was provided at each of the upper and lowerhot air circulation ducts.

Five slits were formed in each of the front wall and the back wall. Tothe slits were fitted nozzles shown in FIG. 7. The injection directionof hot air was toward inside the heat treatment chamber.

Channeling-preventing plates of 15 cm in width were arranged betweenzones and between zone and inner side wall. Thereby, each gap was set at1 cm.

Into the apparatus were fed polyacrylonitrile-based fiber strands (1dtex, 24,000 fibers/strand). The feeding speed of strands was 300 m/hrand a hot air of 1.1 m/sec and 260° C. was fed to the uppermost path.

Hot air of 260° C. was fed to each nozzle at 10 m/sec. Thereby, thespeed of the hot air passing through the lowermost path could be kept at80% of the speed of the hot air passing through the uppermost path.

1. A heat treatment apparatus for oxidation having: an oven foroxidation having a heat treatment chamber having a plurality of slitsthrough which fiber strands running horizontally leave or returnedstrands enter and capable of sending hot air vertically from above thefiber strands to allow the fiber strands to have oxidation, and a meansfor feeding hot air into the heat treatment chamber, a plurality ofreturning rollers which are provided at the two outsides of the oven foroxidation and which return the fiber strands entering and leavingthrough said slits, into the oven for oxidation, wherein each gap formedbetween fiber strands and each side wall of heat treatment chamberparallel to the running direction of fiber strands running in the heattreatment chamber, or each gap formed between fiber strands and achanneling-preventing plate interposed between the side wall and thefiber strands in parallel to the running direction of fiber strands isset at 150 mm or less and a heating means is provided at the side wallsor in the slits and wherein a heating means is provided at said sidewalls or in said slits.
 2. A heat treatment apparatus for oxidationaccording to claim 1, wherein the channeling-preventing plate hasair-passing holes.
 3. A heat treatment apparatus for oxidation accordingto claim 1, wherein the oven for oxidation comprises: a heat treatmentchamber wherein hot air passes from the above toward the bottom, anupper duct formed at the top of the heat treatment chamber, a lower ductformed at the bottom of the heat treatment chamber, and a hot aircirculation duct connecting the upper duct and the lower duct.
 4. A heattreatment apparatus for oxidation according to claim 3, wherein an airrate-controlling member is provided in the hot air circulation duct. 5.A heat treatment apparatus for oxidation according to claim 3, whereinhot air circulation means are provided at the top and bottom of the hotair circulation duct.
 6. A heat treatment apparatus for oxidationaccording to claim 5, wherein each hot air circulation means is a fan ora blower.
 7. A heat treatment apparatus for oxidation according to claim6, wherein the blower is a multi-blade blower having two inlets for hotair.
 8. A heat treatment apparatus for oxidation according to claim 1,wherein air-passing members having an opening ratio of 50% or more areprovided above lower air-passing plates provided at the bottom of theheat treatment chamber and apart from the lower air-passing plates by 20mm or more.
 9. A heat treatment apparatus for oxidation according toclaim 1, wherein the heating means is a hot air duct formed outside eachside wall of the heat treatment chamber.
 10. A heat treatment apparatusfor oxidation according to claim 1, wherein the heating means is aheater formed each side wall of the heat treatment chamber.
 11. A heattreatment apparatus for oxidation according to claim 1, wherein theheating means is nozzles for feeding hot air into the heat treatmentchamber, provided in all or part of the plurality of slits.
 12. A heattreatment apparatus for oxidation according to claim 11, wherein the hotair has a temperature higher than the temperature of the heat treatmentchamber.
 13. A heat treatment apparatus for oxidation according to claim11, wherein the nozzles have a mechanism of feeding, into the heattreatment chamber, not only the hot air injected from the nozzles butalso the air present in the vicinity of each nozzle and drawn by saidhot air.
 14. A heat treatment apparatus for oxidation according to claim11, wherein the nozzles are provided only in the slits through whicheach fiber strand enters the heat treatment chamber.
 15. A heattreatment apparatus for oxidation according to claim 11, wherein atleast one of lower slits corresponding to 70% of the total slits has anozzle capable of injecting air outside the heat treatment chamber. 16.An operating method of a heat treatment apparatus for oxidation having:an oven for oxidation having a heat treatment chamber having a pluralityof slits through which fiber strands running horizontally leave orreturned strands enter and capable of sending hot air vertically fromabove the fiber strands to allow the fiber strands to have oxidation,and a means for feeding hot air into the heat treatment chamber, and aplurality of returning rollers which are provided at the two sides ofthe oven for oxidation and which return the fiber strands entering andleaving through said slits, into the oven for oxidation, wherein eachgap formed between fiber strands and each side wall of heat treatmentchamber parallel to the running direction of fiber strands running inthe heat treatment chamber, or each gap formed between fiber strands andchanneling-preventing plate interposed between the side wall and thefiber strands in parallel to the running direction of fiber strands isset at 150 mm or less and the plurality of slits are each provided witha nozzle capable of injecting hot air toward the oven for oxidation, inwhich operating method the speed of the hot air fed from the nozzles iscontrolled and thereby the speed of the hot air passing through thefiber strands other than the uppermost fiber strands is kept at 20% ormore of the speed of the hot air passing through the uppermost fiberstrands.